Bicycles have proved to be very efficient vehicles for converting human energy into mechanical energy in order to produce self-propelled motion. Most bicycles include a metallic frame that comprises a set of tubes that are welded together. The wheels, the drive assembly, and the steering assembly are all mounted to the frame to complete the bicycle. Recently, there have been significant efforts to substitute frames formed of composite material for frames formed of metal. An advantage of a composite frame is that it offers as much structural strength as a metal frame and weighs significantly less. Moreover, composite frames, unlike conventional frames, do not rust and corrode when exposed to the elements. These advantages are expected to help make composite-frame bicycles very popular for use as mountain bicycles and other types of bicycles where it is desirable to have a frame with significant mechanical strength and that can withstand the rigors of contact with water, mud, rocks, and other wearing material.
Composite bicycle frames are typically formed of nonmetallic material that is shaped in a mold. Owing to the expenses associated with forming the molds and the costly composite materials, it has proved very expensive to build these bicycles. It is also expensive to provide the differently sized composite frames required to build bicycles for large numbers of cyclists who are themselves of different statures. Some bicycle manufactures have attempted to overcome this problem by providing composite frames with metal fittings and fixtures that can be adjustably set to accommodate the needs of differently sized cyclists. However, this solution has not proved to be wholly satisfactory. The addition of these metal components increases the weight of the assembled bicycle, detracting from the advantages of the composite frame.
Another drawback to composite frames is their high cost necessitated by labor-intensive construction and the expensive composite materials used to provide sufficient strength. Frame strength is especially critical with negative-space bicycles, i.e., bicycles with an open or C-shaped frame that does not include a top tube, seat post tube, or frame stays. The bending and torsional forces that must be counteracted are more highly concentrated with these bicycles.